1. Field
This invention relates to an overpressure device for use in a liquid infusion system to detect an overpressure condition in the system.
2. Prior Art
There are a number of intravenous solution pumps of various kinds which have been disclosed or are in use currently whose function is to deliver discrete volumes of fluids at precise rates to a patient. The use of such pumps greatly reduces the time and attention of nurses who are responsible for administration of parenteral solutions to patients as compared to the standard gravity feed system of administration where the nurse has to check constantly to see that a preadjusted flow rate is being maintained.
As sometimes happens during the administration, the tubing becomes occluded if the patient inadvertently lies on the tubing of the administration set, or the tubing may become pinched by a bed rail; or the infusion needle may become lodged into a muscle instead of the vein of the patient. If a pump were to continue forcing fluid through the tubing under such circumstances, it could result in harm to the patient.
This overpressure condition can be noted by means of auditory or visual signals built into a pump which provide a warning of the condition. There are also various means associated with I.V. pumps which sense an overpressure condition and by appropriate electrical circuitry result in stopping or greatly reducing the pumping action until the condition is corrected. One such means is disclosed in U.S. Pat. No. 3,985,133 wherein an occlusion or overpressure in a set causes a slowing down or stalling of the shaft on the pump motor. This reduction in shaft rotation is detected by a pair of light detectors which triggers the occlusion alarm. Another means for occlusion detection is disclosed in U.S. Pat. No. 3,731,679 wherein a syringe pump is associated with a device having four channels, one being connected to the pump, another to a supply of fluid, a third connected to tubing leading to the patient and the fourth being closed at its outer end. If the solution being administered becomes overpressured, it backs up into the fourth channel (which is normally filled with air) until contact is made with an electrode positioned within the channel. This activates a circuit which results in stopping the motor to the pump.
An apparatus is disclosed in U.S. Pat. No. 3,456,648 which is designed to monitor predetermined critically high levels of venous pressure during infusion of solutions. The apparatus includes a manometer connected to the tubing of the infusion set and an optical sensor slidingly supported on the manometer at any predetermined point. If the venous pressure should reach a critical pressure, the solution will rise up the manometer tube and when light from the optical sensor is reflected by the presence of the solution, a valve is actuated to stop the flow of solution into the patient. The aforementioned devices of U.S. Pat. Nos. 3,731,679 and 3,456,648 have deficiencies which prevent them from being entirely acceptable in overpressure detectors for intravenous infusion sets. They are susceptible to air being bled into the infusion line which could result in an air embolism in the patient and the sensors could be triggered if drops of solution were to come in contact with them as a result of inadvertent jarring of the devices even though no overpressure condition exists.
Formerly an I.V. pump available from Sigmamotor included th capability for detecting overpressures in an administration set. The set contained a translucent vertical connector in the tubing with a horizontal closed ended tubular branch of the same bore size extending horizontally from the middle of the connector. An optical sensor positioned intermediately on the branch detected the presence of liquid forced into this branch as a result of overpressure in the set. The major drawback with this design is again the possibility for inadvertently setting off the alarm indicating an overpressure condition should droplets be flicked into the area of the branch monitored by the sensor as a result of the unit being jarred.
These and other deficiencies are essentially eliminated by employing an improved overpressure device in an infusion set as detailed in the disclosure and claims which follow.